The present invention is generally related to a high isolation antenna and more particularly to an antenna which provides high isolation and wide bandwidth for transmit and receive operations, while at the same time providing for a structure which requires minimal area and volume.
In certain radio, microwave, or optical communications applications it is typically necessary to have an antenna system capable of providing sufficient isolation between transmit and receive operations.
Full duplex radio or microwave, has typically relied on isolation techniques, such as, frequency separation or antenna (optical collection) separation. Frequency separation techniques rely on filtering, or separating signals of differing frequencies received via the antenna, before further processing of the signals. Antenna separation techniques are directed toward separating the transmit and receive antenna elements so as to avoid any interference between the two and to provide for optimum gain for both transmit and receive.
Frequency separation techniques typically require the use of high-performance filters. However, these filters are typically bulky and expensive and often are not feasible given the cost constraints at hand. For example, waveguide filters are available which provide excellent performance but are bulky and expensive. Compact, three-dimensional guided-wave filters made using titania (TiO2) as a dielectric, instead of air, are also available however the cost and dimensional tolerances often make them less than ideal.
There are a number of known antenna separation techniques. The highest isolation (on the order of 70 dB) is typically achieved by physically separating the transmit antenna and the receive antenna so that each has separate and distinct high-gain collection optics. Unfortunately, in order to achieve equally high gain in both the transmit and receive systems, a great deal of space is consumed as the required area and volume necessary to provide separate antenna systems will at least double.
Another approach has been to simultaneously feed a main aperture (reflector or lens) with two orthogonally polarized beams, one for transmit and one for receive. A more specific implementation of this technique has been to feed an array of square or nearly square patch antennas at right angles. If the array is large enough, it can serve as the main aperture; if not, it can act as a feed to a larger reflector or lens. One drawback to this technique is that the intrinsic isolation between the vertical and horizontal feeds to a single patch, is typically very low (20 dB or less). Isolation can be increased with the use of patch array techniques. However, as patch antennas are typically narrowband in nature, both transmit and receive signal responses tend to be very narrowband.
Further, there are quasi-optical feed-plus-main-aperture schemes for antenna separation which exist. For example, it is known to use a polarizer to split/combine the beams to/from the transmitter antenna and the receiver antenna. FIG. 1 illustrates a quasi-optical split polarization antenna separation scheme in which the transmit antenna and the receive antenna have orthogonal polarization. In this, there is provided a transmit horn 10 having a transmit signal radiation pattern 11 and a receiver horn 20 having a receive signal radiation pattern 21. A polarizer 15 receives the transmit signal T from the transmit horn 10 then splits the transmit signal T and distributes it to the main aperture lens 25. Polarizer 15 also receives a received signal R from the main aperture lens 25 and distributes it to the receive horn 20. This arrangement is rather bulky, although not so much as if completely separate optics are used. The polarizer must typically be quite large, often almost as large as the main aperture, in order to assure uniform illumination and preserve polarization
Another antenna separation technique utilizes a split-focus main reflector in which a main aperture is made up of a large array of polarization-dependent and position-dependent mini-reflectors. The focal point of the split-focus main reflector is different for the two polarizations. Two small feed antennas that are spatially separated by an amount considerably smaller than the diameter of the main aperture, can then be used for transmit and receive operations. Since each mini-reflector is itself a dual-polarized antenna which differs from its neighbors, implementation can be rather complex and difficult to achieve.
Both design and manufacturing costs tend to be quite expensive where a large main aperture is used. Furthermore, in both of the above quasi-optical split-feed antenna separation techniques, substantial effort/expense is typically required to design and engineer the angularly separated transmit and receive housings.
Thus, given the above noted shortcomings of the prior art, an unaddressed need exists in the industry to address the aforementioned, as well as other, deficiencies and inadequacies.
The present invention provides a common focus antenna for use in radio frequency, microwave or optical applications. Briefly described, in architecture, a preferred embodiment of the common focus antenna can be implemented as follows. There is provided a substrate having a first surface on which a metal film is attached. Three slot antenna sets are formed in the metal film, and a lens is attached to a second surface area of the substrate. The slot antenna sets are generally arranged on the metal film so that two of the antenna sets are parallel to each other while the third antenna set is positioned between the parallel antenna sets and perpendicular thereto.
Other systems, methods, features, and advantages of the present invention will be or become apparent to one of ordinary skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present invention, and be protected by the accompanying claims.